Colchicine Modulates the Actin Cytoskeleton by Direct Binding to the Monomer and Facilitating Polymerization

Actin, the most abundant intracellular protein, exists in a monomeric globular form (G-actin) or as polymerized filamentous actin (F-actin), and is essential for cell morphology, motility, and intracellular transport. Colchicine is a well-established anti-inflammatory drug primarily known for binding tubulin and inhibiting microtubule polymerization, yet its full mechanism of action remains unclear. Here, we investigated whether colchicine directly modulates actin cytoskeleton dynamics. Using human monocytic and murine B-lymphoma cell lines, combined with in vitro biochemical and biophysical assays, we found that colchicine binds directly to G-actin with submicromolar affinity, enhances actin polymerization, and stabilizes F-actin. Colchicine treatment in cells shifted the F-/G-actin ratio toward the filamentous form, increased cortical actin organization, and altered cell mechanical properties. Thermal shift assays confirmed increased actin stability, while molecular docking identified two potential colchicine-binding sites-one at the ATP-binding cleft in G-actin and another at the intermonomeric interface in F-actin. These findings reveal a previously unrecognized actin-modulatory role of colchicine, providing mechanistic insight into its anti-inflammatory effects and suggesting potential applications in diseases involving actin cytoskeletal dysregulation.